Medical Devices Require Radiation-Tolerant Memory

TORONTO – One of the biggest subsets of the Internet of Things is wearables, and within that segment are devices that monitor health and physical activity. While many of these applications are aimed at consumers who want to track fitness and other measurements of the quantified self, there are also specialized medical applications that are more focused and complex.

Flash memory, such as NOR flash and SPI flash memory, has found use in portable medical devices that include heart-rate monitors, blood analyzers, digital thermometers, and portable defibrillators. A great deal of focus is put on form factor and power consumption of memory -- how do you provide enough computing power in a small device and extend battery life?

But in the case of medical devices, there’s also the issue of safety, especially with the advent of smarter devices that are worn close to or can be implanted in the human body. Many of these devices include wireless communication, so standards have been developed to ensure the safety of those wearing devices. The IEEE 802.15.6-2012 standard, for example, addresses security, reliability, power, quality of service, data rate, and interference protection so these wireless devices and sensors can be used for medical purposes.

Some medical devices are single use and produced in large volume, but more intelligent, high-value devices are reusable. And more importantly, they may also require sterilization in order to be used in the human body, and that process poses a danger to memory -- it can’t withstand the gamma radiation needed to sterilize a device to the degree these environments require.

Radiation has always been a threat to memory technologies, but historically the use cases have applied to vehicles travelling at very high altitudes and satellites and other equipment being launched into space, noted Jim Handy, principal analyst at Objective Analysis. In the early days of digital cameras, not only was there concern that photographic film might not survive more powerful security inspection equipment at airports, but that the data on the flash cards in cameras might be wiped out as well.

A new type of memory developed by Adesto Technologies has been tested and proven to endure the sterilization required for medical applications. While the company’s focus has been on low-power memory, it has also spent a number of years investigating the tolerance of its proprietary memory to radiation.

Adesto CEO Narbeh Derhacobian said there is no memory technology today that can survive sterilization through radiation, and this has been a barrier to putting more intelligence into medical devices. Its conductive bridging random access memory (CBRAM), which is non-volatile, uses typical memory cells to store digital ones and zeroes. Adesto adds a dielectric layer in its manufacturing process. A small electrical voltage is used to change the resistance of the memory cell between high and low resistance to distinguish between ones and a zeroes.

Essentially, said Derhacobian, the fundamental physics of the memory is different, and information is stored differently on the chip to make it tolerant to radiation.

Some of the testing of Adesto’s CBRAM was done by Nordion, in Ottawa, Canada. Emily Craven, manager of sterilization science, said testing electronics is a relatively new business for the company, and she was surprised at how well Adesto’s memory held up to gamma radiation exposure. “It’s a very big leap forward.”

Craven said historically electronics, including computer parts, can’t tolerate sterilization through radiation. Steam is generally used instead, but that creates its own set of problems. The reason why radiation works well for sterilization is that it’s a clean process for the product, and allows them to be immediately placed in hospitals.

Normally the medical products tested are high volume, single use items, but there are low volume, high volume implantable items such as pacemakers that require this sterilization, said Craven. Adesto’s CBRAM was first tested at 25 kiloGray; exposure was doubled to 50 kGy. It even tolerated 200 kGy, she said, which is more than most devices can withstand.

Craven said CBRAM’s tolerance to radiation opens up the medical device world for a whole set of new possibilities that been haven't seen before, such as “smart” syringes. “We’re really excited about it.”

@goafrit My comment must have been unclear. The embedded plutonium in a working pacemaker device is perfectly safe for the patient and for the surrounding environment. The concern was that a severe accident or cremation could breach the container and release free plutonioum into the environment which would be a serious issue.

>> While the dead patient wouldn't care, the release of plutonium into the environment during cremation was a serious concern.

That is interesting that someone can have that while alive. Then on death, the toxicity level could harm others. This calls for the need to think through materials before they are deployed in products.

Another challenging issue is the need for medical devices to tolerate cremation (or accidents) without releasing toxic materials even after the patient dies. In the instance of plutonium powered heart pacemakers this was a serious issue. While the dead patient wouldn't care, the release of plutonium into the environment during cremation was a serious concern. Physical shielding accounted for a significant portion of the bulk of the device.

My experience in the medical device is that the components command good premium compared to the consumer market. So, this can be done. I know for example in MEMS, you can sell a unit of XL for $60 compared with $0.60 you can get in the consumer market.

I remember I've read article on Scientific American IBM at that time was investigated MEMS memory - essentially atomic-size abacus. I never heard what happend to that technology, probably dead-ended. Sad, if they've kept the development, it could be highly tolerant to radiation memory.

@resistion: You have made an excellent point!! If there is a way to control the radiation such that the radiation serves its purpose without damaging the semiconductor while keeping the cost lower than what it would be with the CBRAMs, that should make the case for it.

Are the CBRAMs equivalent to FLASH functionally? Currently what kind of memory chips being used in space equipments, for which the radiation threats are similar? I have heard of radiation hardened FPGAs being used but do not have much idea about the memory.

If the purpose is sterilization, you have to choose a radiation that kills the germs without killing the CMOS. And that radiation has to be cheaply provided. Generally the thinner the memory layer the less likely the radiation would deposit damaging energy.